"We're going to get into the vehicle tomorrow and get a chance to practice what we're going to experience in a couple of weeks," STS-116 shuttle commander Mark Polansky told reporters at Discovery's Pad 39B launch site.

"The reality is that the displays are the same, it's just lighting so we just adjust that," said Discovery shuttle pilot William Oefelein. He added that the only difference to launch training for night and day liftoffs included sessions in a darkened cockpit simulator and slight changes to post-liftoff fuel tank photography tasks. "Everything else we do, it doesn't matter whether it's day or night."

NASA launched its first three post-Columbia accident shuttle missions in broad daylight to evaluate safety modifications to the orbiters' external fuel tank after investigators traced the 2003 tragedy to tank foam debris. A decision on whether to implement more changes is expected Thursday, NASA officials told SPACE.com.

The STS-116 crew will don their bright orange launch suits early Thursday and climb into Discovery's cockpit and middeck as part of their Terminal Countdown Demonstration Test (TCDT) training.

"I've never been so close to a shuttle that's going to launch," said Fuglesang, who has been an ESA astronaut since 1992 but is making his first spaceflight wit STS-116. "It feels fantastic."

Williams will stay aboard the ISS after the 12-day STS-116 mission as a member of its Expedition 14 crew-commanded by NASA astronaut Michael Lopez-Alegria-which filmed the first-ever live high-definition television broadcast earlier today.

Returning to Earth aboard Discovery in Williams' place will be space station flight engineer Thomas Reiter-also an ESA astronaut-who arrived at the ISS during Discovery's STS-121 mission in July. Russian cosmonaut Mikhail Tyurin completes the Expedition 14 crew.

"Well, 116 is sort of opening up the door to what we're going to be doing," Williams said. "I can't stop forgetting that I'm going to be up there for six months."